Question

I have this struct;

#define BUFSIZE 10
struct shared_data {
    pthread_mutex_t th_mutex_queue;
    int count;

    int data_buffer_allocation[BUFSIZE];
    int data_buffers[BUFSIZE][100];
};

and I want to allocate one of the data_buffers for a process, for that purpose I execute the following function;

int allocate_data_buffer(int pid) {
    int i;
    for (i = 0; i < BUFSIZE; i++) {
        if (sdata_ptr->data_buffer_allocation[i] == NULL) {
            sdata_ptr->data_buffer_allocation[i] = pid;
            return i;
        }
    }
    return -1;
}

but the compiler warns me that I’m comparing pointer to a value. When I put a & in front of sdata_ptr it calms down but I’m not sure if it will work. Isn’t what I wrote above supposed to be true?

Answer 1

Probably because NULL is #define’d to be (void*)0 which means

 if (sdata_ptr->data_buffer_allocation[i] == NULL) {

would be comparing an int to a pointer. Change it to compare to 0 instead.